This invention relates to a method of controlling the flow of current in a winding which forms part of a liquid control value more particularly a spill valve of an engine fuel system.
EP-A-0376493 discloses a method of controlling the flow of current in a winding in which the current is allowed to rise to a peak value and is then allowed to decay initially at a low rate and then at a higher rate until it reaches a value which is below a holding value, the current then being increased to the holding value. The current can be allowed to rise and fall to maintain a mean hold value. The armature which is associated with the winding starts to move under the influence of the magnetic field produced by the winding in the latter portion of the period during which the current is rising to the peak value and reaches its final position at or just before the attainment of the holding value of current. GB-A-2025183 discloses a method of controlling the flow of current in which the current is allowed to reach a high peak value and then before the associated valve reaches its final position, modifying the current flow.
In an engine fuel system it is important to know when a valve member forming part of the control valve attains its closed position and in a fuel system which employs a number of such valves it is important that each valve closes at the same time in its cycle of operation. It is desirable that the valve member should reach its closed position as soon as possible following the initiation of current flow but at the same time it is important to ensure that valve bounce is minimised. The knowledge of the point of valve closure enables the instant of valve closure to be varied to ensure correct operation of the engine.
SAE paper 861049 p153, 154 discusses the detection of valve closure in an engine fuel system and also discusses the adjustment of the start of the valve closure sequence in order to compensate for variation of battery voltage and other variables such as the resistance and inductance of the solenoid of the actuator controlling the valve.
WO87/05662 discloses a system for monitoring the opening of a valve in an engine fuel system, the valve being coupled to the armature of an electromagnetic actuator. The solenoid of the actuator is connected to a low voltage source at the time when the valve assumes its fully open position and this allows detection of a discontinuity in the current flowing in the solenoid. However, the connection of the solenoid to the low voltage source does slow the movement of the valve to the open position.
The object of the present invention is to provide a method of controlling the flow of current in a winding of the kind specified in a simple and convenient form.